Tim O'Reilly speculated why Google is really doing a free 411 service.
In short, I'm speculating that the 1-800-GOOG-411 service is designed to harvest voice data to build Google's own speech database, rather than licensing from Nuance or another player.
Charlie confirmed this at the recent Google Developer Day.
Dr. Norvig said that the primary motivation behind Goog-411 is to provide something useful to Google's users, but the voice data the service collects will certainly help the company improve its voice recognition capabilities.
This isn't surprising - Google has a proven track record of providing useful, free software that is ultimately a vehicle to feed the AdSense cash cow. Perhaps the more interesting question is how Google will put this speech database to work in the future. Such a database would be incredibly useful to deliver contextual AdSense for audio products. Of course, the injection process is a bit more complicated (and less dynamic) in a podcast as opposed to a web page.